The present invention relates to a system for monitoring conditions outside a vehicle, which is adapted to image an object in a predetermined range outside a vehicle and then to distinguish the shape of the object and road from the imaged picture.
Many vehicles are used in our modern society because an automobile is so convenient for transporting persons or articles. Accordingly, many automatic accident avoiding systems are being developed recently. In view of this, development of technologies capable of automatically avoiding accidents without sacrificing the excellent features of automobiles have been conventionally conducted.
For automatically avoiding collision between the vehicle and objects, it is very important to detect an obstacle or obstruction on a path way of the vehicle. In addition, it is necessary to recognize a course along which the automobile runs, and to grasp the position of the object on the road. And thus it is important to judge whether or not the road condition is dangerous. For example, in the case where a road is curved or bent, it is necessary to detect the obstacle along the curve.
Such systems have already been developed as detecting an obstacle by using a radar (radiation detecting and ranging), an ultrasonic wave, a laser (light amplification by stimulated emission of radiation), and etc. However, these systems can detect only the object existing in a specific direction, but not recognize the road shape, nor grasp the positional relationship between the obstacle and the road.
Accordingly, a distance measurement system has recently been used as an effective method. The system images a sight as an object outside the vehicle by an imaging device such as a camera mounted on the vehicle to process the imaged pictures to detect objects such as other vehicles and the road shape to obtain a distance between the vehicle and an object.
Recognition/distance measurement systems using pictures are generally classified into two technical categories. One is to estimate the distance between a running car and the object by measuring a relative distance between a camera position and the image by a single camera. The other is based on a so called stereoscopic method, which obtains the distance between the car and the object by principle of a triangulation after a plurality of pictures are imaged at several positions sequentially changed by a plurality of cameras or the single camera.
As a technology to detect the obstacle or the road shape from a two-dimensional picture of the image taken by a single camera, for example, Japanese patent application laid-open No. 1-242916 (1989) discloses the technique in which a television camera is mounted in a cabin near a center portion at a top of a front window, the obstacle and the white line on the road are detected by using pictures obtained therefrom in dependency on a luminance distribution pattern on a certain survey line in the image and the two-dimensional luminance distribution pattern, and the three-dimensional position of the white line and the obstacle is estimated in dependency on parameters such as mounting position or a directional and visual field of TV cameras.
However, an actual picture of the road has so many objects such as buildings and trees in the surroundings, that it is difficult to precisely detect the various objects such as a running car in front, an oncoming car, a pedestrian, a pole for a telephone or electric light and a white line across a road from such a two-dimensional picture (pattern of feature). Namely, there are circumstances where such technologies cannot be put into practice with sufficient reliability. Furthermore, there is the problem that an estimation of the three-dimensional position has a large error when the three-dimensional position of a white line or the obstacle is estimated from a parameter of the television camera where the surface of the road is uneven, the road has a rising or falling gradient and the vehicle is pitching.
On the other hand, a more precise distance can be obtained by a relative discrepancy of the position of the same object in left and right pictures through the technique of the stereoscopic method of obtaining the distance on the basis of triangulation from a plurality of the pictures.
For example, Japanese patent application laid-open No. 59-197816 (1984) discloses a method for calculating a three-dimensional position of an obstacle by using the principle of triangulation in which two television cameras are mounted on a front part of the vehicle, the obstacle is detected by a two-dimensional luminance distribution pattern with respect to respective images of each television camera, and the positional discrepancy of the obstacle on two pictures is obtained. However, with this prior art, it is difficult to detect the obstacle for respective pictures. Namely, this technology also does not have sufficient reliability as described above.
Further, in Japanese Patent laid open No. 48-2927 (1973) and the Japanese Patent Laid Open No. 55-27708 (1980), two television cameras are attached to right and left ends in front of the vehicle. Each picture is spatially differentiated to extract only a dark/light changing point, and an image scanned by one camera is delayed by a predetermined time to superpose on another picture, thus to extract only a three-dimensional object from the characteristics of a change in brightness of the three-dimensional object of portions in correspondence with each other in two pictures. However, actual pictures are complicated. For example, in the case where a picture has a plurality of three-dimensional objects, a large number of points where the brightness changes appears, so it is impossible to obtain a correspondent relationship with respect to a plurality of three-dimensional objects. Accordingly, even with these technologies, it is difficult to precisely detect the object.
As described above, in actual complicated circumstances, it is extremely difficult to precisely detect the distance, the three-dimensional object, positional relationship or the shape from the imaged picture.